The game plan in advance is definitely a great idea. With a group that size, there's a fine line between wrangling the crowd in such a way that everyone is included, and being a mean ol' drill sergeant that's just barking orders and making it not fun.
If we can prep a list of all the desired sub-groups in advance, we should be able to run through them pretty quickly, if everyone cooperates. Either an electronic list that we send/text to everyone, or a handful of copies of a printed list. Or both.
I might be able to set up my backup camera on a tripod with one light, and have someone (trustworthy) there to mash the shutter button - that would work well for getting portraits of individuals and pairs quickly, while I work on the posed sub-group shots (all the Emmas etc).
My wife has a background in stage show direction and production, so she's pretty proficient about moving things along. If we get a couple Mountain Dews in her, she'll certainly be able to help run the show so I can concentrate on making good photos.